The truncation error in this expansion is bounded by 3εn6/1-εn3 and the recursive process is terminated when this quantity is negligible compared with the machine precision.

The function may fail either because it has been called with arguments outside the domain of definition, or with arguments so extreme that there is an unavoidable danger of setting underflow or overflow.

Note:RDx,x,x=x-3/2, so there exists a region of extreme arguments for which the function value is not representable.
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On entry, y must not be less than 0.0: y=value.
The function is undefined.

7 Accuracy

In principle the function is capable of producing full machine precision. However, round-off errors in internal arithmetic will result in slight loss of accuracy. This loss should never be excessive as the algorithm does not involve any significant amplification of round-off error. It is reasonable to assume that the result is accurate to within a small multiple of the machine precision.